JP2010513622A - Gas dispersion grid for polymerization equipment - Google Patents

Abstract

A gas distribution grid comprising a plurality of trays arranged to form an inverted conical sidewall and attached to each other to form slots in overlapping regions of adjacent trays.

Description

The present invention relates to a gas distribution grid suitable for distributing an upward gas flow into a container containing fluidized polymer.
In particular, the present invention relates to a gas dispersion grid suitable for installation in a fluidized bed reactor for olefin polymerization. The invention also relates to a fluidized bed reactor comprising such a dispersed grid and a gas phase polymerization process carried out in such a fluidized bed reactor.

  With the development of Ziegler-Natta type and more recently metallocene type catalysts with high activity and selectivity, processes for the polymerization of olefins in gaseous media in the presence of solid catalysts have become widely used on an industrial scale. ing. An example of such a gas phase polymerization process involves using a fluidized bed reactor that maintains the bed of polymer particles in a fluidized state by upward flow of fluidized gas.

  During the polymerization, a new polymer is produced by catalytic polymerization of the monomers, and the produced polymer is discharged from the reactor to keep the polymer bed at a constant volume. A continuous upward flow of fluidized gas containing the recirculated gas stream and make-up monomer keeps the fluidized bed containing the growing polymer particles and the bed of catalyst particles in a fluidized state.

  Fluidization of a powdered solid is generally an operation that is easily accomplished by adapting the velocity of the gas stream to the size, shape, and density of the powdered solid. It is desirable to disperse the fluidizing gas uniformly in the fluidized solid bed. In industrial processes, a distributed grid is used to distribute the fluidizing gas to the polymer bed, which also serves as a support for the bed when the gas supply is stopped. Such distributed grids are usually provided with orifices and are located at the bottom of the fluidized bed apparatus.

  Fluidized grids more commonly used in polymerization plants have the shape of a cylindrical disk with a number of through holes drilled so that fluidized gas can flow from the area below the grid to the fluidized polymer bed. To pass through. Such a fluidized grid can also be integrally formed with the reactor wall.

  However, when the fluidized bed apparatus exceeds a certain size, the distribution of the fluidizing gas through the polymer bed becomes more uneven and tends to appear in the bed, particularly around the apparatus wall, in a dense and poorly fluidized region. I found out. Olefin polymerization is an exothermic reaction and local heat spots can appear inside the polymer bed, which can cause softening of the polymer particles and their agglomerates. This phenomenon tends to be more severe when the polymerization is operated in a so-called “condensation mode” and the fluidizing gas also contains a small amount of condensed monomer, and the uniformity of the dispersion of this liquid is impaired, Solid adhesion or agglomeration within the fluidized bed can be caused.

  Another drawback associated with prior art perforated grids is that the through-holes can become clogged by the deposition of polymer particles, which prevents the polymerization apparatus from operating continuously for extended periods of time. Giving larger sized holes solves the clogging problem somewhat, but some polymer particles fall through the holes into the area under the grid, depositing on the walls under the gas distribution plate. There is a possibility of forming. Also, increasing the distance between the holes, i.e. the pitch of the holes, creates stagnant regions between the holes, resulting in the formation of heat spots and polymer mass in the area between the holes. there is a possibility.

In order to solve the above problems, fluidized grids having holes of different shapes, sizes, numbers and distributions have been proposed.
During normal polymerization operation, gas dispersion with caps above the grid holes to solve the risk of clogging the grid holes, especially when the polymer bed falls due to the supply of fluidized recycle gas being stopped Instrument plates are described in several patents. Documents EP-B-088404 and GB-2,271,721 both have caps over the holes in the plate to prevent the particles from falling through the holes for use in a fluidized bed. A gas distributor plate is described.

  Japanese Examined Patent Publication No. 4-42404 (1992) discloses a gas distribution plate in which a roof-shaped overcap is provided on a gas passage hole, and gas flows out from both sides of the cap. Furthermore, Japanese Patent Application Laid-Open No. 1-284509 (1989) discloses a gas distributor plate having an overcap having a shape in which an outer line viewed in a longitudinal section is inclined and rises to cover and protect a gas passage hole. Yes.

  Disperser plates with caps mentioned above help to some extent to prevent the pores from becoming clogged with solids, but do not allow the flowing gas to diffuse evenly through the polymer bed, making the fluidized bed polymerization process efficient. From a driving perspective, it is not satisfactory.

  The disclosure of EP-173261 teaches the insertion of a diffusion plate at the bottom end of a fluidized bed reactor corresponding to a tube through which a gas recirculation stream is passed. Such a diffusion plate improves the uniformity of the gas flow through the fluidizing grid that creates turbulence in the region below the fluidized bed grid. Such a diffuser plate design is such that the gas flow is divided into two main flows: the first is upward and the second is sideways. However, the described embodiment has a tendency for the flat surface of the diffusion plate to collect particulates that are entrained in the circulating gas stream, which can lead to polymer mass growth on the surface of the diffusion plate; There is a high risk of partially blocking the flow of fluidized gas to the polymerization reactor.

  In EP-0856610, there is a gas distributor for a fluidized bed reactor which is composed of an inverted cone having a conicity in the range of 50 ° to 120 ° and which is provided with holes on its sides for passing the fluidizing gas. Are listed. At the apex of such an inverted cone is provided a device for discharging the produced polymer. An additional slot or orifice in the shape of a crown is disposed laterally at the upper end of the conical gas distributor, and the width of such an orifice allows the particulates entrained in the fluidizing gas to pass through, while at the same time Dimensions that prevent the fluidized bed from falling due to gravity during the interruption of the fluidization process. The fluidizing gas flows upward through a narrow gap located between the conical distributor and the reactor wall. The fluidizing grid proposed by EP-085610 has the disadvantage that such narrow gaps through which the fluidizing gas can be easily clogged by particulates entrained in the recirculated gas stream.

  All of these conventional arrangements are complex in structure and difficult to manufacture and handle. Using a series of caps above the grid holes can cause a large increase in the pressure drop of the polymerization apparatus. Further, the cap-covered holes can become clogged with particulates entrained in the fluidizing gas. This is especially true when no cyclone is used in the recirculation gas line to separate particulates entrained in the gas recirculation flow.

European Patent No. 088404 UK Patent Application Publication No. 2,271,721 Japanese Examined Patent Publication No. 4-42404 JP-A-1-284509 European Patent Application Publication No. 173261 European Patent Application Publication No. 085610

  In view of the above-mentioned drawbacks of prior art gas dispersers, it is simple to manufacture, ensures an optimal distribution of gas flow inside the polymer bed, and reduces the risk of pore clogging. The need to provide a fluidized grid is highly felt.

  Accordingly, a first object of the present invention is a gas distribution grid comprising a plurality of trays arranged to form an inverted conical sidewall and attached to each other to form a slot in the overlapping region of adjacent trays. is there.

FIG. 1 shows a fluidized bed reactor for the gas phase polymerization of olefins comprising the gas dispersion grid of the present invention. FIG. 2 shows the bottom of the fluidized bed reactor of FIG. 1: FIG. 2a is a side view of the dispersion grid and FIG. 2b is a plan view of the dispersion grid. FIG. 3 shows a radial cross-sectional view of a single slot formed by overlapping two adjacent trays in the distributed grid of FIGS. 2a and 2b. FIG. 4 shows a tangential cross-sectional view of the slot of FIG.

  The gas distribution grid of the present invention is particularly suitable for uniformly dispersing an upward gas flow in a container containing a fluidized polymer. This is therefore conveniently located at the bottom of the container containing the fluidized polymer particles.

  The grid includes a plurality of overlapping trays arranged such that the structure of the fluidized grid has a substantially inverted conical shape. In order to best understand the scope of the claimed arrangement, the following definitions are given for “gas dispersion grid”, “tray”, and “overlapping region”.

  The expression "gas dispersion grid" has the function of distributing an upward flow of gas that can keep the polymer bed in a fluidized state without optionally excluding the supply of liquid with the gas flow. Indicates a grid or plate. As known to those skilled in the olefin polymerization art, the presence of a small amount of liquid monomer in the fluidized gas stream generally refers to a polymerization process operated in "condensation mode".

  The term “tray” means a flat part, such as a plate or sheet, that can be easily deformed on one of its sides when overlapped with the next adjacent tray to form one or more slots. To do.

  The term “overlapping area” refers to the area where the first tray extends above the second tray so that both trays can be secured together to form a slot in this overlapping area. .

  The trays of the present invention can be made of any useful material that can withstand the temperature and pressure of the polymerization process. It is preferable to use steel trays because they can be easily manufactured and can be placed on each other to form slots in their overlapping regions. According to one embodiment, successive trays overlap to form an annular module of trays, i.e., adjacent trays are placed together to form a ring structure. The circular modules of these trays can be placed side by side radially to form the overall structure of the gas distributor. Such an annular module is mounted on a suitable annular support so that the gas distribution grid can also support the bed of polymer particles during reactor startup or shutdown. Such an annular support is held in a state where it is supported by a rod-like member protruding from the bottom wall of the container containing the fluidized polymer.

  The tray modules are generally arranged to form inverted conical sidewalls having vertices of 100 ° to 160 °, preferably 120 ° to 150 °. Preferably, the tip of the cone is cut to form an opening through which the polymer particles can be ejected from the container.

  Depending on the diameter of the vessel in which the gas disperser is installed, 2-6 circular modules of the tray can be used to form the conical structure of the dispersive grid. When using trays with equivalent surface area, the outer peripheral module must contain a greater number of overlapping trays relative to the inner central module. This is the result of the vessel or reactor containing the fluidized polymer having a circular cross section.

  In general, each annular module includes at least six trays, preferably the number of trays is in the range of 10-80. Clearly, the greater the number of trays used to form the annular module, the greater the number of slots formed on the annular module. The slots are formed by overlapping adjacent trays to provide a tangential gas outlet to the surface of the adjacent trays, as will be described in detail with reference to the accompanying drawings.

  According to a preferred embodiment of the invention, in the overlapping area of adjacent trays, the first tray forms the top of the slot, while the next tray forms the bottom of the slot. Preferably both trays are deformed to form a row of slots.

In general, there are a number of slots in the range of 3-15 slots in the overlapping region of two adjacent trays. Preferably, the slots are of similar size and shape.
The pressure drop that exists between the inlet and outlet sides of the dispersion grid can force the fluidizing gas to flow upward through the row of slots.

The gas distribution grid of the present invention will now be described in detail with reference to the accompanying drawings, which are representative examples of the scope of the present invention and are not intended to limit the scope of the present invention.
FIG. 1 shows a fluidized bed reactor 1 comprising a fluidized bed 2 of polymer, a gas distribution grid 3 of the present invention, and a velocity reduction or release zone 4 disposed above the polymer bed 2.

  The velocity reduction zone 4 is generally of increased diameter compared to the diameter of the fluidized bed portion of the reactor. In addition to unreacted monomers, the gas stream discharged from the top of the velocity reduction zone 4 may also contain an inert condensable gas such as propane, and an inert non-condensable gas such as nitrogen. is there. Such a gas stream is compressed, cooled and recycled to the bottom of the fluidized bed reactor: from the top of the velocity reduction zone 4, the gas stream passes through the recycle line 5 to the compressor 6 and then to the heat exchange. Sent to the vessel 7. If appropriate, the recirculation line 5 is fitted with a line 8 for supplying monomers, molecular weight regulators and possibly inert gases. The gas stream is cooled through heat exchanger 8 and sent through line 9 to the bottom of the fluidized bed reactor. The recycle gas can be cooled below the dew point of one or more gaseous components, where appropriate, to operate the reactor with condensed material, i.e., in condensed mode.

In general, the various polymerization catalyst components are fed to the fluidized bed reactor 1 through a line 10 which is preferably arranged in the lower part of the fluidized bed 2.
The introduction point of the line 9 in the reactor is located directly below the dispersion grid 3 and the introduction direction of the line 9 is such that it causes a “centrifugal effect” in the area under the dispersion grid 3.

According to another aspect, the release zone 4 may be omitted by a specific design of the gas distributor 3 that reduces the risk of clogging the holes by particulates entrained in the recirculation gas.
The dispersion grid 3 of the present invention is supported by a plurality of rod-like members 11 protruding from the bottom wall of the reactor in the area below the dispersion grid. A portion corresponding to the center of the gas distributor 3 is provided with an annular opening 12 through which polymer particles can be withdrawn from the fluidized bed continuously or intermittently (preferably in a continuous mode). The opening 12 of the gas distributor 3 converges into a conduit 13 for discharging polymer particles from the reactor. The discharged particles are then fed to a degassing and extrusion facility (not shown).

  Figures 2a and 2b show a more detailed view of the gas distribution grid 3 according to the invention. From FIG. 2a, it is clear that the gas distributor has the shape of a truncated cone, ie a wall with a trapezoidal cross section. In this embodiment, the apex angle of the truncated cone is 120 °.

  The gas disperser includes dendritic annular modules 14a, 14b, 14c of the tray 15 that are connected together to form a frustoconical sidewall. The annular modules 14a, 14b, 14c are composed of plate-shaped trays 15, which are placed on an annular support so that each tray is connected to two adjacent trays. The annular module is held in a state supported by a rod-like member 11 protruding from the bottom wall of the reactor under the gas dispersion grid.

  When the trays are detachably connected to each other, it is very easy to assemble and disassemble the gas disperser of the present invention or replace several trays for maintenance reasons.

  In the particular embodiment of FIG. 2, the peripheral annular module 14a includes 44 trays, the central annular module 14b includes 30 trays, and the inner annular module 14c includes 18 trays.

  The number of slots 16 increases from the inner annular module to the peripheral annular module so that the number of slots per area is held substantially constant throughout the grid. However, the module design can be easily adapted to all needs by increasing or decreasing the number of trays in each annular module. In the particular embodiment of FIG. 2, each tray 15 includes seven slots 16 of the same cross section.

  The slot 16 is formed to provide a tangential gas outlet to the surface of two adjacent trays 15. Thus, the slot 16 can form a swirling motion of the gas flow above the gas dispersion grid 3 installed at the bottom of the fluidized bed reactor of FIG.

  As mentioned above, the fluidizing gas is introduced through a conduit 9 directly under the dispersion grid 3, the direction of introduction being such that it causes a “centrifugal effect” in the area under the dispersion grid 3. Furthermore, the gas flow introduced through the conduit 9 has the same direction as the slots 16 on the distribution grid 3, which facilitates the introduction of gas into the slots 16.

FIG. 3 shows a radial cross-sectional view of a single slot 16, ie, a cross-sectional view in a direction orthogonal to the direction of gas flow through the slot 16.
The slot 16 is formed by overlapping two adjacent trays 15a and 15b. Each tray forms a lower portion of the slot on one side and an upper portion of the slot on the opposite side. This arrangement is substantially the same for all trays in the gas distributor. Specifically, the upper end of the slot 16 is formed by the first tray 15a, and the lower end of the slot 16 is formed by the second tray 15b attached to the first tray 15a. The first tray 15a is modified to form a slot 16 having a substantially rectangular cross section. The first tray 15 a defines the top and sides of the rectangular slot 16, while the second tray 15 b defines the bottom side of the rectangular slot 16. The width of the slot 16 in this embodiment is greater than twice its height.

  FIG. 4 shows a tangential cross-sectional view of the slot 16, that is, a cross-sectional view in a direction along the direction of gas flow through the slot 16. Similarly, it can be seen that the upper portion of the slot 16 is formed by one tray and the lower portion is formed by the next tray.

  The slot 16 is comprised of three parts substantially along the flow direction: an inlet part, a central part, and an outlet part. In the central part, the trays 15a and 15b are substantially parallel, the length of the central part is greater than its height and its inclination with respect to the surface of the tray is substantially zero. The inlet part has a height that narrows along the flow direction, while the outlet part rises slightly and is formed only by the lower tray 15b. The axis of the slot 16 is tangential to the surfaces of the trays 15a, 15b.

  The inlet of each slot 16 is kept clean by introducing fluidized gas introduced from the recycle gas line of the reactor. Preferably, the slots 16 located on the opposite side of the same tray 15 are not aligned and staggered. In this manner, the area between the slots in the downstream series of slots can be kept clean by the gas continuously blown from the upstream series of slots.

  The slot may have any shape, such as a triangle, rectangle, semi-circle, or circle, and is not limited to a particular shape. It is preferable to arrange slots having a substantially rectangular shape.

  The slots are preferably identical in cross section and dimensions. However, the slot cross-section and dimensions can be different between the inner part of the grid and the outer part of the grid near the reactor wall. The slot length can be adjusted by increasing or decreasing the overlapping area of adjacent trays. Thus, a more flexible arrangement is provided without adjusting the thickness of the gas distributor itself or without providing a cap over the slots in the grid. By selecting trays with different shapes or cross sections, the gas distributor can be easily adapted to different process conditions. The dispersed grids of the present invention can be successfully used in many devices involving fluidization of polymer powders (not necessarily involving monomer polymerization reactions). As an example, the dispersion grid may be placed at the bottom of a dryer that holds polymer particles that are dried by an upward continuous flow of a hot drying gas such as nitrogen in a fluidized state.

In particular, the following advantages can be obtained by using the gas disperser of the present invention:
(1) By ejecting fluidized gas tangentially from the slot, a swirl motion is formed in the polymer bed near the fluidized grid, thereby minimizing the heat spot at the bottom of the fluidized bed. Such swirling motion of the gas flow also contributes to improving the uniformity of gas dispersion inside the fluidized polymer bed.

  (2) The slanting of the slot with respect to the longitudinal axis of the vessel or reactor prevents the polymer particles from penetrating deeply into the slot, thereby minimizing the risk of clogging the dispersion grid.

  (3) Unlike the arrangement of the prior art, the tangential flow of gas discharged from the slot continuously strikes the peripheral edge of the dispersion grid, resulting in a significant reduction in solid deposition at the peripheral edge. (Minimize heat spot).

  When the bottom of the fluidized bed reactor is adapted for olefin polymerization, the dispersion grid can optimally disperse the gaseous monomer inside the fluidized polymer bed, thereby eliminating the shortcomings of prior art gas dispersers. A reliable and reliable polymerization process.

  Accordingly, the second object of the present invention is to provide a gas distribution grid located at the base thereof, a gas circulation system for cooling and recirculating unreacted gas from the top of the reactor to the distribution grid, and reaction A conduit for continuously discharging the polymer from the vessel is attached and the dispersive grids are arranged to form an inverted conical sidewall and are attached to each other to form a slot in the overlapping area of adjacent trays A fluidized bed reactor for the gas phase polymerization of α-olefins, comprising a plurality of trays.

  Referring to the apparatus of FIG. 1, the gas distribution grid 3 has a conical shape that surrounds the inlet 12 of a discharge conduit 13 that is used to discharge polymer particles from the reactor 1. Preferably, the inlet 12 of the discharge conduit 13 is arranged in the center of the distribution grid 3.

  The discharge conduit 13 includes adjusting means 18 such as a discharge valve suitable for adjusting the mass flow rate of the polymer discharged from the reactor 1. The opening of the discharge valve 18 is continuously adjusted to keep the height of the fluidized polymer bed inside the reactor constant.

  The discharge conduit 13 may be formed with a uniform diameter, but preferably includes a further portion having a diameter that decreases in a downward direction. The control valve 18 is preferably arranged corresponding to a throttle between the larger diameter portion and the smaller portion, as shown in FIG.

The fluidized bed reactor of FIG. 1 with the gas dispersion grid of the present invention has one or more formulas: CH ₂ ═CHR, where R is hydrogen or a hydrocarbon group having 1 to 12 carbon atoms. It is particularly suitable for industrial use in a continuous process for the gas phase polymerization of certain olefin monomers. Optionally, gas phase polymerization can be carried out in the presence of one or more C ₂ -C ₈ alkanes or cycloalkanes as inert condensable gases.

  Accordingly, a further object of the present invention is fitted with a fluidizing grid located at its base, a gas circulation system for cooling unreacted gas from the top of the reactor and recirculating it to the dispersion grid. A gas phase process for polymerizing one or more α-olefins in the presence of a polymerization catalyst in a fluidized bed reactor, wherein the overlapping regions of adjacent trays are arranged to form inverted conical sidewalls. Wherein the unreacted gas is continuously flowed through the slots of a distributed grid comprising a plurality of trays attached to each other to form slots.

  The polyolefin produced is continuously discharged from the fluidized bed reactor 1 by a discharge conduit 13 protruding from the apex of an inverted cone formed by arranging a plurality of trays.

  The discharged polyolefin 13 is transferred to a separation tank (not shown) by a discharge conduit 13, where the polymer obtained is separated from unreacted monomers and inert gaseous compounds, and the separated gaseous components flow. Continuously recirculated to the bed reactor 1.

The polymerization conditions are those that are conveniently adapted to a gas phase reactor for the polymerization of olefins, ie temperatures in the range of 60-120 ° C. and pressures in the range of 5-40 bar.
The gas phase polymerization process of the present invention can be combined with conventional methods operating in slurry, bulk, or gas phase to carry out a sequential multi-stage polymerization process. Accordingly, one or more polymerization stages can be provided upstream or downstream of the polymerization apparatus of the present invention, operating in a loop reactor, or a normal fluidized bed reactor, or a stirred bed reactor. In particular, gas phase polymerization reactors having interconnected polymerization zones as described in EP-782587 and EP-1012195 can be advantageously arranged upstream or downstream of the device according to the invention.

A gas phase polymerization process can produce a large number of olefin powders with low particulate content and optimal particle size distribution. The α-olefin preferably polymerized by the process of the present invention has the formula CH ₂ ═CHR, where R is hydrogen or a hydrocarbon group having 1 to 12 carbon atoms. Examples of polymers that can be obtained are
High density polyethylene (HDPE having a relative density higher than 0.940) such as ethylene homopolymer and ethylene copolymer with α-olefins having 3 to 12 carbon atoms;
Low density linear polyethylene (LLDPE having a relative density lower than 0.940) and very low density and ultra, composed of ethylene copolymers with one or more α-olefins having 3 to 12 carbon atoms Low density linear polyethylene (VLDPE and ULDPE having a relative density below 0.920 and up to 0.880);
An elastomeric terpolymer of ethylene and propylene and a small proportion of diene or an elastomeric copolymer of ethylene and propylene having a content of units derived from about 30 to 70% by weight of ethylene;
A crystalline copolymer of propylene and ethylene and / or other α-olefins having a content of units derived from isotactic polypropylene and propylene greater than 85% by weight;
An isotactic copolymer of propylene and an α-olefin such as 1-butene having an α-olefin content of ≦ 30% by weight;
An impact propylene polymer obtained by sequential polymerization of propylene and a mixture of propylene and ethylene containing up to 30% by weight of ethylene;
An amorphous copolymer of propylene and ethylene and / or other α-olefins containing atactic polypropylene and units derived from more than 70% by weight of propylene;
It is.

  The gas phase polymerization process described herein is not limited to the use of any particular group of polymerization catalysts. The present invention is useful in any exothermic polymerization reaction using any catalyst, whether it is supported or unsupported, and whether it is a prepolymerized form.

The polymerization reaction can be carried out in the presence of a highly active catalyst system such as a Ziegler-Natta catalyst, a single site catalyst, a chromium-based catalyst, a vanadium-based catalyst.
The Ziegler-Natta catalyst system is obtained by reacting a group 4-10 transition metal compound of the periodic table of elements (new notation) with an organometallic compound of group 1, 2, or 13 of the periodic table of elements. Containing catalyst.

In particular, the transition metal compound can be selected from Ti, V, Zr, Cr, and Hf compounds. Preferred compounds are of the formula: Ti (OR) _n X _{yn where} n is in the range 0 to y; y is the valence of titanium; X is halogen; R is 1 to 10 A hydrocarbon group having 1 carbon atom, or a COR group). Among these, titanium compounds having at least one Ti-halogen bond such as titanium tetrahalide or halogen alcoholate are particularly preferred. Preferred specific titanium compounds are TiCl ₃ , TiCl ₄ , Ti (OBu) ₄ , Ti (OBu) Cl ₃ , Ti (OBu) ₂ Cl ₂ , Ti (OBu) ₃ Cl.

Preferred organometallic compounds are organic-Al compounds, especially Al-alkyl compounds. The alkyl-Al compound is preferably selected from among trialkylaluminum compounds such as, for example, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. . Alkyl aluminum halides, alkylaluminum hydrides, or alkylaluminum sesquichlorides such as AlEt ₂ Cl and Al ₂ Et ₃ Cl ₃ can also optionally be used in admixture with such trialkylaluminum compounds.

Particularly suitable high yield ZN catalysts are those in which a titanium compound is supported on an active form of magnesium halide, preferably on an active form of MgCl ₂ . In particular, to produce a crystalline polymer of an olefin of CH ₂ CHR (where R is a C _{1 to} C ₁₀ hydrocarbon group), an internal electron donor compound can be supported on MgCl ₂ . Typically these can be selected from esters, ethers, amines and ketones. In particular, it is preferable to use compounds belonging to 1,3-diether, cyclic ether, phthalate, benzoate, acetate, and succinate.

If it is desired to obtain highly isotactic crystalline polypropylene, in addition to the electron donor present in the solid catalyst component, an external electron donor (ED) can be added to the aluminum alkyl cocatalyst component or polymerization reactor. In addition, it is recommended to use it. These external electron donors can be selected from among alcohols, glycols, esters, ketones, amines, amides, nitriles, alkoxysilanes, and ethers. The electron donor compound (ED) can be used alone or mixed with each other. Preferably, the ED compound is selected from among aliphatic ethers, esters, and alkoxysilanes. Preferred ethers are C ₂ -C ₂₀ aliphatic ethers, and in particular cyclic ethers having preferably 3 to 5 carbon atoms, such as tetrahydrofuran (THF), dioxane.

Another useful catalyst is a vanadium-based catalyst comprising the reaction product of a vanadium compound and an aluminum compound, optionally in the presence of a halogenated organic compound. In some cases, the vanadium compound can be supported on an inorganic carrier such as silica, alumina, magnesium chloride. Suitable vanadium compounds are VCl ₄ , VCl ₃ , VOCl ₃ , vanadium acetylacetonate.

Other useful catalysts are based on chromium compounds such as chromium oxide on silica, also known as Philips catalysts.
Other useful catalysts are single site catalysts, such as metallocene bases comprising at least one transition metal compound having at least one π bond, and a compound capable of forming at least one alumoxane or alkyl metallocene cation. The catalyst system.

  The catalyst can suitably be used in the form of a prepolymer powder previously produced during the prepolymerization stage using the catalyst described above. The prepolymerization can be performed by any suitable process, for example, polymerization using a batch process, semi-continuous process, or continuous process in a liquid hydrocarbon diluent or in the gas phase.

Claims (18)

  A gas distribution grid comprising a plurality of trays arranged to form an inverted conical sidewall and attached to each other to form slots in overlapping regions of adjacent trays.   The gas distribution grid according to claim 1, which is arranged at the bottom of a container containing fluidized polymer.   The gas distribution grid of claim 1, wherein the vertex of the inverted cone ranges from 100 ° to 160 °.   The gas distribution grid of claim 1, wherein an annular module of trays is formed by superimposing successive trays.   The gas distribution grid of claim 4, wherein each annular module includes at least six trays.   6. A gas distribution grid according to claim 5, wherein each annular module comprises 10 to 80 trays.   5. A gas distribution grid according to claims 2 and 4, wherein the annular module of the tray is supported by a rod-like member protruding from the bottom wall of the container containing fluidized polymer.   The gas distribution grid of claim 1, wherein in such overlapping regions, the first tray forms the top of the slot and the next tray forms the bottom of the slot.   The gas distribution grid of claim 1, wherein there are a plurality of slots in the range of 3-15 slots in the overlapping region of two adjacent trays.   The gas distribution grid of claim 1, wherein the slot is configured to provide a tangential gas outlet to the surface of the adjacent tray.   The gas distribution grid of claim 1, wherein each tray forms the bottom of the slot on one side and the top of the slot on the opposite side.   The gas distribution grid of claim 1, wherein the slot has a substantially rectangular shape.   The gas distribution grid of claim 1, wherein the axis of the slot is tangential to the surface of the adjacent tray.   The gas distribution grid of claim 2, wherein the container containing fluidized polymer is a dryer.   A gas dispersion grid located at the base, a gas circulation system for cooling and recirculating unreacted gas from the top of the reactor to the dispersion grid, and for continuously discharging the polymer from the reactor Α-, with a conduit attached, wherein the distribution grid includes a plurality of trays arranged to form an inverted conical sidewall and attached to each other to form a slot in an overlapping region of adjacent trays. Fluidized bed reactor for gas phase polymerization of olefins.   The reactor according to claim 15, wherein the inlet of the conduit for discharging polymer is located in the center of the dispersion grid.   In a fluidized bed reactor fitted with a fluidization grid located at its base and a gas circulation system for cooling the unreacted gas from the top of the reactor and recirculating it to the dispersion grid, the polymerization catalyst A gas phase method for polymerizing one or more α-olefins in the presence of a gas phase process arranged to form sidewalls of inverted cones and attached to each other to form slots in overlapping regions of adjacent trays. Wherein said unreacted gas is continuously flowed through a slot in a distributed grid comprising a plurality of trays.   The process of claim 17, wherein the polymer is continuously discharged from the reactor by a discharge conduit protruding from the apex of the inverted cone.

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